Manufacture of articles comprising cellulose



Patented Jan. 16, 195 l '7 UNITED. STATES PATENT OFFICE MANUFACTURE OF ARTICLES COMPRISING cELLpLosE Wayne; A. Sisson, Silverside, and Mamerto M.

Cruz, Jr., Wilmington, Del., assignors to American Viscose Corporation, Wilmington, DeL, a

corporation of Delaware Application November 30, 1944, Serial No.'566,016

No Drawing.

12 Claims.

This invention relates to methods of handling acid-moist articles comprising partially regenerated cellulose whereby to protect the same from deterioration due to acid-degradation of the cellulose, upon completion of regeneration of the cellulose.

Articles formed from viscose by extruding or casting the viscose into an acid setting bath always carry an appreciable quantity of adhering acid from the bath. For reasons of economy,

the viscose is extruded or cast into the acid bath continuously, and the articles thus formed are passed through the bath and withdrawn therefrom rapidly, so that the viscose is only partially coagulated or "set up when the article emerges from the bath. Articles so obtained comprise a skin of cellulose hydrate enveloping fluid viscose or only partially decomposed xanthate, dependence being placed upon penetration of the adhering acid through the skin to complete the de-.,

composition of the cellulose xanthate. While the chemical reactions leading to such xanthate decomposition are in progress, the presence of s that the acid is prevented from exerting a degrading action on the cellulose. It is another object of the invention to prolong the period during which acid-moist articles comprising partially regenerated cellulose may be stored safely, prior to washing thereof, without inhibiting decomposition of any cellulose Xanthate present.

the acid is necessary, and the acid does not exert an appreciable over-all degrading effect on the cellulose which has been regenerated. However, after allcf the cellulose xanthate has been decomposed, the free sulphuric acid attacks the cellulose, with the result that the quality of the article is eifected. For instance, in the case of filamentary material, if free acid is permitted to remain on the material for any appreciable time after the cellulose is regenerated, acid degradation or tendering of the cellulose is soon evidenced by a lowering of the D. P. number (Degree of Polymerization) indicating a change in the molecular structure, and resulting in diminished tensile strength and extensibility of the filaments.

For this reason, it is the common practice to subject acid-moist articles comprising regenerated cellulose to washing with water as soon as practicable after withdrawal of the article from the acid bath and completion of regeneration of the cellulose, in order to remove the acid therefrom.

However, it frequently happens that there is a considerable time lapse between withdrawal of the articles from the acid bath, and washing thereof, during which time any cellulose xanthate present is completely decomposed, and the regenerated cellulose is subject to acid attack. Such delays may be occasioned by a temporary breakdown of the washing equipment, by the necessity-for storing the acidmoist articles during The instant invention is based upon our discovery that the rate at which dexanthation of cellulose xanthate proceeds to completion in the presence of acid, and the onset of acid degradation of the regenerated cellulose are functions.

of the pH on the article, both dexanthation and acid degradation being accelerated at extremely low pH, especially at higher temperatures such as may prevail in storage cabinets or the like,

and depending to some extent on the length of timeduring which the article is permitted to stand in the acid moist condition.

The acid-laden articles as they come from the setting bath normally have a pH below about 0.5.

comprising partially regenerated cellulose for any appreciable length of time, an equilibrium can .be established between the rate at which dexanthation is completed and the rate at which acid-degradation is effected, by controlling the pH on the article so that it is raised to and maintained at a value greater that 1 and less than 7. It is preferred to maintain the pH on the article at from 2 to about 3.5, and specifically at about 2.5, because at such a pH value acid-deg- 'article is stored, and the concentration of the acid on the article, while at'a pH lower than 2 acid-degradation may be quite noticeable at the higher temperatures, say temperatures of C.

or higher. Illustratively, and preferably, this objective may be accomplished by permitting the article to stand in the presence of an aqueous solution of sodium sulfate. Instead of an aqueous solution of sodium sulfate, solutions of other sodium salts may be substituted including sodium phosphate, acetate, phthalate, etc. Again, bufferin systems may be used. The concentration of the aqueous sodiumsalt solution may vary somewhat depending upon the particularsalt employed but in general solutions of 10 to 30% concentration are serviceable. For example;

when aqueous solutions of sodium sulfate are employed, solutions of 15 to 20% concentration are preferred.

We found, for example, that when wound packages (weight approximately 3.5 lbs.) of freshly spun acid-moist yarn produced from vise cose in accordance with the wet spinning process, and having a pH of below 0.5 were immersed in six liters of a 16% aqueous solution of sodium sulfate having a pH of 6.1, at room temperature, a pH of about 3.1 was established after about one hour. The pH gradually dropped to about 2.5. After standing in the solution for about 530 hours, the yarnafter washing with Water and drying at room temperature, was found to have a D. P. number (Degree of Polymerization) as measured by the cuprammonium viscosity method (Battista Ind. & Eng. Chem. Analytical Ed. v01. 16, pg. 351, June 1944) of 399, as contrasted with the D. P. number of the material before immersion, which was 412, i. e., after standing for 530 hours the drop in D. P. number was only 3.9%, and the yarn had a dry tensile strength of 2.66 gms./denier and dry extensibility of 18.4%; wet tensile strength of 1.66 ems/denier and wet extensibility of 27.5%. n the other hand, when similar wound packages of acid-moist yarn, produced in the same manner, and having a pH of below 0.5 were stored in a cabinet at room temperature and exposed to circulating air at relative humidity of 90%, for-530 hours, the yarn had a D. P. number-of 221, that is, the drop in D; P. of the yarn at the end of of 10.8%, wet tenacity of 0.84 gms./denier and wet extensibility of 9.4%.

If the pH on the articleis adjusted to and maintained at a value of greater than 1 and less than 7 in accordance with this invention, partially regenerated cellulose articles which carry adhering acid may be stored safely for prolonged periods, even though the pH is on the acid side. This is indeed surprising in view of the general knowledge as to the deterioration of cellulose at acid pHs and the recognition of the art as to the ill-effects incident to departing 'from the standard practice of washing cellulose articles obtained from viscose by the wet spinning method within a short period of time after formation thereof.

'In addition to preventing or markedly inhibiting acid degradation of cellulosic articles during storage, the invention has ancillary advantages. Thus, when wound packages of filamentary material are treated the yarn does not dry out and crystallization of salts, such as may have been carried from the spinning bath and which cause breaking of the yarn, does not occur within the package, with the result thatthe yarn finally obtained is of good quality and characterized by uniform strength and shrinkage and dyeing capacities along the entire length thereof. The invention is of special value when acid-moist filamentary material derived from viscose and destined for use in the manufacture of tires is stored, because even a very small percentage of acid-degradation has a markedly pronounced deleterious effect on the flexing life of'tire cord.

The acid-moist article comprising cellulose may be steeped or immersed in the aqueous sodium salt solution,- or the latter may be sprayed or otherwise applied to the article after withdrawal thereof from the setting bath. For example, the solution may be sprayed or poured on filamentary material as it is withdrawn from the spinning bath, in which case the solution remains on the material after collection thereof. The aqueous sodium salt solution may serve as aplasticizing agent during stretching of the filaments and may be applied to the material as it advances over the stretching reel or other stretching device of a continuous spinning system. The solution may also be applied to filamentary material produced by a continuous spinnin method, to complete dexanthation of the cellulose xanthate prior to subjecting the material to the usual after-treatments. When the solution is applied as a plasticizer during stretching or to complete dexanthation or when applied for both purposes in succession, it is preferably heated to a temperature of from about 60 C. to just below C.

Certain variations and modifications may be made in practicing the invention without departing therefrom and it is to be understood that We are not to be limited except by the spirit and scope of the appended claims.

We claim:

1. The method of handling acid-moist articles freshly prepared from viscose, which articles comprise at least some partially regenerated cellulose and have a pH of less than 1 after withdrawal'thereof from an acid setting bath, to effect complete regeneration of the cellulose by the acid while inhibiting acid degradation of the cellulose during and after such regeneration, and while the articles are held under acidic conditions comprising storing the article, at room temperature'and under atmospheric pressure, in a weakly acidic aqueous sodium salt solution of from 10 to 30% concentration to raise the pH on the article to a value of greater than 1 and less than 7, and keeping the article in that solution at room temperature and under atmospheric pressure at least until the cellulose is completely regenerated.

The method of handling acid-moist articles freshly prepared from viscose, which articles comprise at. least some partially regenerated cellulose and have a pH of less than 1 after withdrawal. .thereof from an acid setting bath, to effect complete regeneration of the cellulose by the acid while inhibiting acid degradation of the celluloseduring and after such regeneration, and whilethe articles are held under acidic conditions comprising storing the article, at room temperature and under atmospheric pressure, in a weakly acidic aqueous sodium sulfate solution of from 10 to 30% concentration to raise the pH on the article to a value of greater than 1 and lessthan 7, and keeping the article in that solution-at room temperature and under atmospheric pressureat least until the cellulose is completely regenerated.

3. The method'of handling acid-moist articles freshly prepared from viscose, Which articles while the articles are held under acidic conditions, comprising storing the article, at .room temperature and under atmospheric pressure, in a weakly acidic aqueous sodium salt solution of a concentration inthe range of from to 30% and such that the pH on the article is raised to and maintained at a value of from about 2 to 3.5, and keeping the article in that solution at room temperature and under atmospheric pressure at least until the cellulose is completely regenerated.

4. The method of handling acid-moist articles freshly prepared from viscose, which articles comprise at least some partially regenerated cellulose and have a pH of less than 1 after withdrawal thereof from an acid setting bath, to effect complete regeneration of the cellulose by the acid while inhibiting acid degradation of the cellulose durin and after such regeneration, and while the articles are held under acidic conditions comprising storing the article, at room temperature and under atmospheric pressure, in a weakly acidic aqueous sodium sulfate solution of from to concentration to raise the pH on the article to a value of from about 2 to 3.5, and keeping the article in that solution at room temperature and under atmospheric pressure at least until the cellulose is completely regenerated.

5. The method of handling acid-moist filamentary material freshly prepared from viscose, which material comprises at least some partially regenerated cellulose and has a pH of less than about 1 after withdrawal from an acid setting bath, to effect complete regeneration of the cellulose by the acid while inhibiting acid degradation of the cellulose during and after such re- Which material comprises at least some partially regenerated cellulose and has a pH of less than about 1 after withdrawal from an acid setting bath, to effect complete regeneration of the cellulose by the acid while inhibiting a-cid degradation of the cellulose during and after such regeneration and while the material is held under acidic conditions, which comprises collecting the a filamentary material in the form of a wound package, storing the package, at room temperature and under atmospheric pressure, in a weakly I acidic sodium salt solution of a concentrationin the range f from 10 to and such that the pH on the material is raised to and maintained at a value of from about 2 to 3.5, and keeping the package in that solution at room temperature and under atmospheric pressure at least until the cellulose is completely regenerated. t 8. The method or handling acid-moist filamentary material freshly prepared from viscose, which material comprises at least some partially regenerated cellulose and has a pH of less than about 1 after withdrawal from an acid setting bath, to effect complete regeneration of the cellulose by the acid while inhibiting acid degradationof the cellulose during and after such regeneration and while the material is held under acidic :conditions, which comprises collecting the generation and while the material is held under acidic conditions which comprises collecting the filamentary material in the form of a wound package, storing the package, at room temperature and under atmospheric pressure, in a weakly acidic sodium salt solution of from 10 to 30% concentration t raise the pH on the material to a value of greater than 1 and less than 7, and keeping the package in' that solution at room temperature and under atmospheric pressure at least until the cellulose is completely regenerated.

6. The method of handling acid-moist filamentary material freshly prepared from viscose, which material comprises at least some partially regenerated cellulose and has a pH of less than about 1 after withdrawal from an acid setting bath, to effect complete regeneration of the cellulose by the acid while inhibiting acid degradation of the cellulose during and after such regeneration and while the material is held under acidic conditions, which comprises collecting the filamentary material in the form of a wound package, storing the package, at room temperature and under atmospheric pressure, in a weakly acidic sodium sulfate solution of from 10 to 30% concentration to raise the pH on the material to a value of reater than 1 and less than '7, and keeping the package in that solution at room temperature and under atmospheric pressure at least until the cellulose is completely regenerated.

'7. The method of handling acid-moist filamentary material freshly prepared from viscose,

filamentary, material in the form of a wound package, storing the package, at room temperature and under atmospheric pressure, in a weakly acidic sodium sulfate solution of from 15 to 20% concentration to raise the pH on the material to a value of from about 2 to 3.5, and keeping the package in that solution atroom temperature and under atmospheric pressure at least until the cellulose is completely regenerated.

9. The method of handling acid-moist filamentary material freshly prepared from viscose, which material comprises at least some partially regenerated cellulose and has a pH of less than about 1, after withdrawal thereof from an acid setting bath, to effect complete regeneration of the cellulose while inhibiting acid degradation of the cellulose during and after such regeneration, and while the material is held under acidic conditions, comprising storing the material, at room temperature and under atmospheric pressure on a thread-advancing reel in a Weakly acidic aqueous sodium salt solution of from 10 to 30% concentration to raise the pH on the material to a value of greater than 1 and less than '7, and keeping the material on the reel in that solution at room temperature and under atmospheric pressure at least until the cellulose is completely regenerated.

10. The method of handling acid-moist filamentary material freshly prepared from viscose, which material comprises at least some partially regenerated cellulose and has a pH of less than about 1, after withdrawal thereof from an acid settin bath,to effect complete regeneration of the cellulose while inhibiting acid degradation of the cellulose during and after such regeneration, and while the material is held under acidic conditions, comprising storing the material, at room temperature and under atmospheric pressure on a thread-advancing reel in a weakly acidic aqueous sodium sulfate solution of from 10 to 30% concentration to raise the pH on the material to a value of greater than 1 and less than '7, and keeping the material on the reel in that solution at room temperature and under atmospheric pressure at least until the cellulose is completely regenerated.

1 The met ne e e rmei fi ementary material, freshly prepared from jvis'jcose,

which inate'riafcomprises at least some, partially regenerated 'e'euulqse and has a pH of less than about 1, after Withdra'wal'jthreoffrom an acid setting bath, to effect completeregeneratioh'of the cellulose Whileinhibitihg' acid degradation ,of the cellulose during and'after such regeneratioh, andwhile the materiallis held'nnderacidic conditions, comprising [storing the ,materialj'jat room temperature 'and under atmqspheric ipressure on a thread-[advancing reel in jgaflweakly acidic aqueous sodium salt solutionflof [a concentrationin the range'bf from10ftoj30%fl and such that the pH o'ri the material is. raised to" and maintained ata value ofirom about 2 to 3.5,jand keeping the material on. the reel inthatsolution at room temperature and under atmospheric pressure at least'untilthe' cellulose is completely regenerated.

12. The method of handling acid-moist filamentary material freshly preparedlfrom viscose, which material comprises at least some partially regenerated cellulose and has a pH of less'than about 1, after withdrawal'thereof from an acid setting bath, to efiect complete regeneration of the cellulose whilev inhibiting acid degradation of the cellulose during and, after such regeneration, and while, thefmaterial is held under acidic conditions, comprising storing. the material,at room 8 t m ati ean cun e at esah i re s r On a '-advanci ng reelfin aweakly acidic aqueous sodium" sulfate fsolutign pffrom" 15' to" 20% concentration [to' raise thejpI-Ionv the material to a valu'fo'f jtromjabout 2j to 3.5, and keeping the jfn aterial' o'nfih {reel in that solution "at room temperature andjunder atmospheric pressure at glea'stnntil the-cellulose is completely regenerated. W J' M YWAYNEA. SISSON.

M. CRUZ, J3.

REFERENCES .CITED ='I h e.,folloyiring references are ofrecordin the fileof this patent:

UNITEDSTATES PATENTS 

1. THE METHOD OF HANDING ACID-MOIST ARTICLES FRESHLY PREPARED FROM VISCOSE, WHICH ARTICLES COMPRISE AT LEAST SOME PARTIALLY REGENERATED CELLULOSE AND HAVE A PH OF LESS THAN 1 AFTER WITHDRAWAL THEREOF FROM AN ACID SETTING BATH, TO EFFECT COMPLETE REGENERATION OF THE CELLULOSE BY THE ACID WHILE INHIBITING ACID DEGRADATION OF THE CELLULOSE DURING AND AFTER SUCH REGENERATION, AND WHILE THE ARTICLES ARE HELD UNDER ACIDIC CONDITIONS COMPRISING STORING THE ARTICLE, AT ROOM TEMPERATURE AND UNDER ATMOSPHERIC PRESSURE, IN A WEAKLY ACIDIC AQUEOUS SODIUM SALT SOLUTION OF FROM 10 TO 30% CONCENTRATION TO RAISE THE PH ON THE ARTICLE TO A VALUE OF GREATER THAN 1 AND LESS THAN 7, AND KEEPING THE ARTICLE IN THAT SOLUTION AT ROOM TEMPERATURE AND UNDER ATMOSPHERIC PRESSURE AT LEAST UNTIL THE CELLULOSE IS COMPLETELY REGENERATED. 